Normal hair can be so fine and limp, and so lacking in body that the hair does not hold a hair set well. Furthermore, the hair can become even less bodied and can be weakened further as a result of being subjected to chemically active hair treatments, such as permanent waves and tints. Additionally, hair can be weakened even further by other contributing factors, such as bleaching by sun exposure and/or chlorinated swimming pool water.
Normal hair is usually hydrophobic. However, many of the chemically active hair treatments remove the natural hydrophobic components from the hair. As a result, as the hydrophobicity of the hair decreases, the relative porosity of the hair increases and the hair tends to absorb water and swell more readily. In such a weakened and porous state, the water-swollen hair is more vulnerable to stretching and breaking.
Hair setting is basically the process of shaping wet hair by the steps of stretching the hair by curling the hair, fixing the hair in place by drying, then combing to give the finishing touches to provide the desired hairstyle. In particular, the setting of wet hair can be accomplished by making flat curls from strands of hair and fixing the curls with hairpins to produce "pin curls". Similarly, the wet hair can be set by using any of a variety of rollers or curlers to mechanically fix the hair. In either case, the winding of the wet hair is followed by drying, either by ambient air drying, electric drying or hot air drying.
The inherent problem encountered in hair setting is the natural tendency of the hair to return to its natural shape. For example, the set hair returns to its natural shape almost immediately if moistened. Likewise, high humidity conditions accelerate the tendency of the hair to return to its natural shape. Therefore, intensive efforts have been directed toward providing a hair set with sufficient holding power to maintain the designed hair style until at least the next shampoo, and, therefore, giving the hair set a degree of permanency.
As indicated by the natural tendency of hair to return to its natural shape, hair is an elastic structure. As a result, the slight deformations in the hair structure resulting from setting the hair are completely reversible. However, the rate of return of the hair to its natural shape is dependent upon the method used to deform, or set, the hair. Hair sets performed with wet strands of hair being rolled tightly, either in curls around the finger or on curlers, followed by drying the hair and unrolling the curlers after drying, corresponds to the release of the hair from a deformation-causing load. The deformation, or set, obtained can last for several days, but the set will not be retained if the hair is wetted.
The observations of hair deformation and relaxation are related to physical and chemical changes in the protein structure level of hair. Sufficient stretching of the hair causes partial transformation of the .alpha.-keratin protein structure of the hair into the .beta.-keratin protein structure of the hair. This structural transformation is accompanied by a shift in relative position of the polypeptide chains that is facilitated by water moistening the hair. The shift in position of the poypeptide chains therefore disrupts the ionic and hydrogen bonds in the hair. During the drying procedure, new ionic and hydrogen bonds are formed that block the return to the .alpha.-keratin protein structure of hair. Gradually, the new protein linkages give way, under natural forces, such that the hair returns to its original state and length. If the hair is moistened, the return to the .alpha.-keratin form is virtually immediate.
Therefore, investigators have sought to delay the combined action of natural forces and moisture that causes the hair to return to its original state by applying solutions containing naturally-occurring or synthetic polymers after the hair is shaped into a desired configuration. When applied to the shaped hair from aqueous or aqueous/alcoholic solutions (setting lotions), the polymers leave a film on the hair, after drying, to help maintain the hair in the previously shaped configuration. The polymeric film promotes cohesion and gives stability to the hair set to maintain the hold of the hair set. The principal objective of a setting lotion is to cover the previously styled hair with an invisible polymeric film that will give the styled hair a degree of rigidity and protect the hair style against wind and humidity.
Hair spray products act in a similar manner. The hair spray products are applied to wet and/or dry hair and contain a polymer, or mixtures of polymers, that remain fixed on the previously styled hair and affect the hair in various ways. For example, a "mechanical" effect is exerted on each individual hair. The film-forming polymers are used to provide a flexible sheath of polymeric film on the shaped hair after drying and, therefore, for mechanical reasons, retard the return of each individual hair to its natural shape. In addition, the polymeric film provides an overall stiffening of the hair. The hair behaves as if the individual hair strands are welded together, and the final hairstyle has better cohesion, therefore resisting the natural forces that return the hair to its natural shape. Finally, the polymeric film protects the hair from humidity. The ability of the polymeric film to attract and absorb water is preferably minimal, such that the polymeric film retards moisture uptake by hair and retards the return of the hair to the .alpha.-keratin hair protein structure.
The general principles of hair setting are thoroughly discussed by C. Zviak, in The Science of Hair Care, Marcel Dekker, pp. 149-181 (1986). Zviak reviews both the polymers used in hair setting products and the formulation principles used to produce a hair set product that provides such beneficial hair set properties as improved hairstyle hold, easy application and combing, quick drying and non-stickiness, good hair body and bounce, increased hair volume and gloss, and hydrophobicity. It is evident that in the formulation of any end-use hair-styling product, some of these benefits must be sacrificed to some degree to achieve a competing benefit. Therefore, the formulation of hair set products has proved difficult, and, as a result, hair set products have been developed in a variety of product forms.
The prior art reveals that nonionic, cationic and anionic polymers have been used in hair set products, with the anionic polymers providing the best hair set results. However, anionic polymers also have disadvantages, such as high water solubility and, therefore, low hydrophobicity, and low substantivity to hair fibers, therefore, easy elimination from the hair by combing and brushing. As a result, investigators have continued to search for compounds and compositions that provide the primary benefit of improved durability of the hair set. As previously mentioned, to overcome some of the inherent disadvantages of the polymers utilized to set the hair, hair set products are made available in diversified forms in an attempt to minimize the drawbacks of the particular polymer used in the formulation. For example, hair set products are available as plasticizing lotions, plasticizing gels, aerosol foams, all-purpose lotions, hair sprays, holding lotions, conditioners and shampoos. In each case, however, the polymer is applied only to previously styled hair to help maintain the hair in the previously styled configuration.
In accordance with the present invention, a new and improved aqueous hair styling aid composition and method have been found wherein thermoplastic, amorphous polyester fixative resins or gums, having a glass transition temperature (Tg) less than about 120.degree. C., is applied to wet or dry hair, preferably wet, before styling the hair in the final, desired configuration and, thereafter, the hair is heated to a temperature at or above the glass transition temperature of the polyester, while the hair is in the desired configuration, to soften the polyester, e.g., with a thermal appliance, such as a blow dryer or a curling iron. The polyester thereafter is cooled to a temperature below its glass transition temperature, e.g., by removal of the thermal appliance, to harden the polyester into a clear, tough polymeric film that provides durable set retention. This process of heating and cooling the applied polyester to set the hair can be repeated many times to reconfigure the hair without degrading the polyester. Further, the polyester can be removed by shampooing to prevent buildup of polymer on the hair.